We have designed a longitudinal study to examine reading (in typically developing and reading disabled children) at critical points during its acquisition in readers learning writing systems that vary in orthographic depth: Finnish, English, and Mandarin Chinese. Our previous cross sectional research in English has identified age- and ability-related differences in both neurobiological and behavioral trajectories;the proposed longitudinal study is aimed at gaining a better understanding of the neurocognitive factors responsible for the observed divergences in the reading skills of normally developing and reading disabled cohorts, and to examine the influence of writing system on these divergences. To that end, we will monitor development during children's initial acquisition of the code (ages 5 to 8 years) and during the attainment of fluency by intermediate level readers (ages 8 to 11 years). Developing proficiency in each longitudinal sample will be assessed with common psychometric, adaptive learning, and neurobiological (ERP and fMRI) measures so that relationships among attained skills, cognitive processing, and cortical organization can be tracked.